"Hashem became angry with Bilam for going." After initially being told by Hashem not to accompany Balak's men, Bilam attempts to convince Hashem to let him go. Hashem permits him to go, yet immediately gets angry at him for actually doing so. How can we fault Bilam if Hashem eventually permitted him to go?
Reb Elchonon Wasserman in his Kuntras Divrei Sofrim explains Hashem's reaction to Bilam's actions by invoking a fundamental principle that permeates our entire relationship with Hashem. The basic requirement incumbent upon every person is to fulfill the will of Hashem. There are two ways for us to determine what Hashem's will is. He can tell us explicitly or we can be expected to figure it out on or our own. Similarly, we find this in inter-personal relationships. Sometimes we express explicitly what we want someone else to do and sometimes we may expect the other person to be able to determine our wishes without being told. Although Hashem may technically have permitted Bilam to go, it should have been obvious to Bilam that Hashem preferred him not to, as was evident from Hashem's initial conversation with him. We are held accountable not only to obey the actual commands of Hashem but also to comform to His will even if not explicitly expressed.
Reb Elchonon further develops this principle that the will of Hashem is also binding as the basis for mitzvos and prohibitions instituted by Chazal. It is difficult for a person to determine on his own how Hashem wants him to act. The only way to determine this is if one has an understanding of Hashem. Just as one who has a close relationship with another person can know what the other person truly wants without being told, so too if one develops such a relationship with Hashem he can know how to act even when not told explicitly. It is only through Torah study that a person can begin to "understand" Hashem and discern His will. Hashem's commands are the laws of the Torah; Hashem's will are the laws of Chazal.
The idea that there is more to Avodas Hashem than the actual commands of the Torah is alluded to in the Torah itself. The mitzvah of Shabbos has very specific halachos from the Torah. These are the actual commands of Hashem. Theoretically a person could "observe" Shabbos by not transgressing these explicit rules, yet such a Shabbos does not conform to the will of Hashem. The Ramban in Parshas Emor illustrates vividly what such a Shabbos would look like. According to Torah law work can be done by a non-Jew on behalf of a Jew. A store could be kept open and all activities that are prohibited from the Torah be done in an abnormal fashion thereby circumventing Chilul Shabbos according to the explicit commands of the Torah. Would such a Shabbos fit the description of "A day of rest dedicated to Hashem"? Clearly not, argues the Ramban. In addition to observing the actual Torah restrictions that govern Shabbos, we are bound to keep Shabbos in a manner that is consistent with the will of Hashem. The term colloquially used, "not Shabbosdik" is a description of the unsaid will of Hashem which is also binding on us.
In the beginning of Parshas Kedoshim we are commanded to be holy. There is a dispute between Rashi and the Ramban how to interpret this obligation. According to Rashi this is referring to observing all the halachos concerning gilui arayos - prohibited marital relationships. Rashi, in other words, understands this pasuk to refer to the kedusha achieved by observing explicit commandments of the Torah in this area. The Ramban, on the other hand, interprets this pasuk as not referring to specific prohibitions, but rather to living a life of holiness as opposed to indulging excessively in worldly pleasures. One can be a "naval birshus haTorah - repulsive yet not violating any specific Torah command." The Ramban here also illustrates vividly the lifestyle of such a person. The one whose entire being is consumed by the pursuit of such pleasures has not technically violated any specific command of Hashem. Yet his lifestyle is not a fulfillment of the will of Hashem.
We can learn from Hashem's reaction to Bilam what is expected of us: absolute commitment to both the explicit commands of Hashem as well as to His unsaid will. We turn to our Torah leaders in every generation for guidance in both of these areas. Only those who understand the explicit word of Hashem will have the proper insight to the appropriate fulfillment of the unsaid will of Hashem.